1. The Field of the Invention
The present invention is related to the field of endodontistry. More particularly, the invention is related to systems and operating methods for the preparation of root canals for obturation. The systems and methods involve the use of at least instruments which are dedicated for specific purposes in the inventive methods and systems and are designed for minimal intrusion into the apical portion.
2. The Relevant Technology
To preserve a tooth with a pulp that is diseased or is potentially diseased, it is generally necessary to remove as much of the pulp material as is possible from the pulp canal of the tooth, to shape the root canal(s) without excessively weakening the root canal walls, to prevent or minimize the presence of bacteria through the use of irrigants and dressings, and lastly, to clean the walls of the root canal(s) by removing the smear layer created during instrumentation of the root canal(s). These steps are all done to prepare the root cavity for sealing or obturation which involves filling the root canal with biocompatible materials, such as gutta percha, before the pulp cavity is sealed, thereby promoting the healing and functional recovery of the tooth. This procedure is referred to as root canal therapy.
As indicated hereinabove, root canal preparation involves pulp removal, cleaning of the root canal walls and shaping of the canal walls. This is typically achieved through a guided procedure with the use of instruments which are moved either manually, mechanically or by combinations thereof These instruments are files or bits that are configured to bore and/or cut. Mechanical instrumentation can be achieved through the use of endodontic handpieces coupled to instruments such as files. The endodontic handpieces can impart rotational motion to a file, reciprocal motion by alternately rotating a file clockwise and counterclockwise, sonic movements or ultrasonic movements.
With regard to operating procedures, there are two basic methods from which all of the canal-preparation techniques can be derived. These methods have been interpreted by various authors in an operational context and also in terms of the instrumentation. The primary conventional systems and methods for removing pulp material from the root canal of a tooth are the apico-coronal (step-back) technique and the corono-apical (crown-down) technique. Although these conventional cleaning techniques both rely generally on sequential increases in the diameter of instruments inserted into the root canal. The step-back technique involves the sequential use of instruments by first inserting an instrument all the way down to the apex of the root canal and then using progressively larger files to clean the root canal. So the step-back technique involves cleaning the root canal from the apex toward the crown. The crown-down technique uses a set of files that are inserted sequentially further and further into the root canal until reaching the apex and then instrumenting along the entire length of the root canal after the apex has been reached. Each technique has its own unique benefits and disadvantages.
In the step-back technique, each file that is sequentially used in the root canal has a larger tip diameter and a larger diameter at the top of the file. First, a series of instruments are inserted all the way to the apex that are increasingly larger until the apical portion is cleaned Then the remainder of the canal above the apical portion is cleaned and tapered by using a series of instruments that are successively larger and shorter. With each increase in diameter, the rigidity increases and the flexibility of the files decreases. As a result, it is not possible for the files to be moved in a manner that enables them to adjust to or to follow the contours of the perimeter surfaces of the root canal. This reduced flexibility also increases the likelihood that the files will fail to contact some portions while removing too much of the surrounding dentin in some areas through excessive abrasion and resulting in overthinning of the walls.
Not only is the completeness effected by the use of a set of files wherein each file is larger and more rigid than the preceding file but the ability to safely move the file within the canal is also limited. More particularly, the increasing rigidity results in decreased ability to negotiate the curves in the canal. Significant problems that can result from inserting increasingly rigid files and also from initially inserting a file all the way down to the apex includes laceration and transportation of the apical foramen, as well as misdirection and perforation of the wall.
The apex can be perforated by extrusion of the infected material through the apex due to the force exerted by the file on the material as the file is pushed downward to reach the apex. As a result, the periapical region can be invaded and contaminated. The potential for extruding infected material through the apical foramen of a necrotic tooth during the initial insertion of a file instrument all the way down to the apex is a particular disadvantage of the step-back technique. Another disadvantage is that the procedure has identical steps for working in either necrotic or vital root canals. In addition to exposing the tissue surrounding the tooth to the infected material, apical perforations may allow irrigants, filling or obturating material to flow out of the apex. Such apical perforations, as well as wall perforations, may delay tooth healing and may compromise the outcome of the therapy.
Perforations can also occur due to a failure to maintain a proper working length of the instrument during the procedure. As the canal is widened, curvatures are straightened thereby decreasing the required working length needed for the instrument to work. To properly determine the appropriate working length, many radiographs must be taken throughout the operation as the canal is continuously being modified, which alters the length. The time required to obtain the x-ray photographs or images and to adjust the working length of the instruments by repositioning the stops can result in a lengthy process. The step-back technique is also time intensive because a large number of instruments are required to complete the root canal therapy.
Another problem is the formation of ledges which can occur when a practitioner attempts to insert a file as far as the apex and the file is too inflexible to properly curve with the root canal or move around a protrusion. When a file is too inflexible to curve or flex as needed and is halted prematurely, the downward pressure exerted on the file, in conjunction with the tendency of the file to straighten itself, causes the tip of the file to dig into the side of the root canal and form a ledge. Such ledges are difficult to bypass; and if the ledge occurs very close to the apex, the ledge may give the practitioner the mistaken impression that the apex has been reached.
The crown-down technique was developed for several reasons. It was desired to shape the canal xe2x80x9cconicallyxe2x80x9d so as to keep the diameter of the foramen as straight as possible. The crown-down technique was also developed to prevent the discharge of septic material or obturation material from the apex after the initial canal-preparation step and to prevent subsequent vertical condensation due to the vertical pressure used to obturate the canals with heated gutta-percha. Additionally, the crown-down technique was intended to reduce the number of instruments utilized compared with the step-back technique. However, as discussed hereinbelow, significant potential problems may inherently result from use of the crown-down technique.
The crown-down technique generally involves the use of a set of file instruments that are incrementally inserted further and further into the root canal until reaching the apical portion. A file is first used that is sufficiently large that it binds near the top of the root canal. Then an incrementally smaller file is used so that it binds further down in the root canal. The files that are sequentially used may be incrementally longer or the files may have the same length and be further inserted into the root canal due to their increased narrowness. Once the root canal has been sequentially cleaned along its entire length down to the apex, then a file is inserted down to the apex that it capable of abrading against all of the surfaces of the root canal to eliminate the stepped configuration that has been created. Root canal cleaning procedures that are referred to as crown-down methodologies also often involve the use of a series of instruments after reaching the apex that extend to the apex and have an increasingly larger tapers to finish cleaning and shaping the root canal.
One example of the operational deficiency of the crown-down method lies in its association with instruments made of nickel/titanium Based on the greater flexibility of files formed from nickel/titanium compared with files formed from steel, proponents of the crown-down method in conjunction with nickel/titanium files assert that such files can better follow the curvatures of a root canal. Additionally, it has been asserted that such files are more likely to stay in the center of the root canal, thereby decreasing the likelihood of ledging or perforating the root canal walls. The ability of a nickel/titanium file to stay in the center is not necessarily desirable, in view of the morphology and perimetrical variety of root canals, and particularly the upper two-thirds of root canals which are typically laminar. In fact when rotation is imparted to an instrument that stays in the center of the canal, the file instrument works simultaneously and indiscriminately on all of the walls within reach of the file. Since root canal walls do not have equal thicknesses in all directions and at all different points along a root canal, some walls can be overthinned or perforated, while other walls remain untouched.
Moreover, because nickel/titanium files are more flexible than steel files, they tend to follow the path of least resistance and therefore cannot be used, in the same way as steel files, to be applied actively and intentionally by the operator. As a result, even when the operator knows the thickness of a particular portion, such as an interference or obstruction which the operator desires to rectify or straighten, the operator lacks the freedom to aggressively drive the file as needed and clean the portions that are difficult to reach. Accordingly, when a nickel/titanium file is used to clean a non-cylindrically shaped root canal, the file moves only at the center of the canal and/or the area of least resistance and fails to remove all of the necrotic tissue.
Some problems encountered in application of crown-down methodologies include overthinning of root canal walls, perforation of a root canal wall, excessively weakening of the walls of the tooth or a failure to fully contact all of the canal walls. These problems can be easily caused by the passive, self-guiding use of nickel/titanium files, particularly when utilizing instruments with progressively larger tapers in the transition from the first instrument to the next one in the set.
Overthinning can occur due to the indiscriminate thinning of the walls of the root canals by maintaining a file instrument in a central location during working rotation. Such overthinning can have devastating results. The inability to adequately direct a file used in accordance with the crown-down technique based on the practitioner""s knowledge of the relative thicknesses of the portions of canal walls is a significant disadvantage of the technique.
Lateral perforation results from the formation of a borehole that increases in size until a hole is formed in the side of the root canal through the dentin and cementum around a root canal. Similarly, dangerous overthinning may occur when the borehole increases in size such that it extends into the cementum or very close to the cementum but has not yet created a hole in the side of the root canal then the root canal. Such lateral perforations and areas and that have been overthinned may be obscured from the x-ray due to concavities or curvatures in the root canal. As a result, the practitioner may not realize that the borehole has a formed a hole in the side of the root canal or extends into the cementum and may therefore mistakenly conclude that the root canal treatment has been successful. Infective bacteria that remained in the root canal, perhaps in the portions that were not contacted with the files, as well as toxins produced by the bacteria may then permeate through the cementum and cause infection or other complications.
An example of a cross-section of a laminar-type root canal cleaned by the crown-down technique which may result in successful root canal therapy since the instrumentation has not resulted in a perforation and the cementum has not been exposed is shown in FIG. 15D of U.S. Pat. No. 6,045,362. Although, problems such as perforations or overthinning have been avoided, FIG. 15D shows that large portions of the root canal remain untouched despite the change in morphology through the formation of large borehole. Note that the change in the morphology of the canal shown in FIG. 15D of U.S. Pat. No. 6,045,362 resulting from crown-down technique instrumentation occurs due to drilling in a passive, circular manner, especially when instruments are used having gradual and progressive tapers. The failure to contact significant portions of a root canal while forming a large borehole in a root canal is a very typical result of the crown-down technique since most root canals can be characterized as a laminar-type root canal.
It would be preferable to avoid the risk posed by failing to contact significant portions of the root canal. Since the practitioner is prevented from removing and essentially all pulp material, the practitioner cannot be assured of the reliability of the treatment. Additionally, the practitioner may not suspect that the working instruments have failed to contact every segment of the root canal since the canal has been instrumented from its top to its apex. Use of a set of files with increasingly greater tapers further contributes to a potentially incorrect conclusion that cleaning by such a conventional process has resulted in removing all material from the root canal. Further, the x-ray view of the tooth, as with the step-back technique, may give the incorrect impression that the root canal had been cleaned. It should also be remembered that while rotation of a set of passively actuated files, in the center of the canal, especially those with increasingly greater tapers, in accordance with the crown-down technique, may yield a configuration as shown in FIG. 15D of U.S. Pat. No. 6,045,362 and result in successful root canal therapy, there is a significant hazard of forming lateral perforations and overthinning due to the passivity of the instruments when linked to canal diameters and wall thicknesses that are still statistically unknown.
As in the configuration shown in FIG. 15D of U.S. Pat. No. 6,045,362, the configuration shown in FIG. 15E of U.S. Pat. No. 6,045,362 may also result in successful root canal therapyxe2x80x94but only for canals of the wholly tubular type. Although, the borehole does not extend through the dentin and into the cementum, the diameter of the preparation or borehole is nevertheless significantly larger than that of the original root canal was. The excessive thinning of the dental wall may result in significantly weaken the resistance of the walls to the stress of chewing, and may also cause a fracture of the root.
From the above discussion, it is clear that the actual morphology of the canals is not sufficiently considered when using the crown-down technique. More particularly, when files are used with successively larger tapers, each file, if actuated passively, is primarily limited to being rotated without substantial lateral movements guided by the operator. Since the majority of files are of the laminar type, this limitation poses a significant problem Without the ability to laterally move the files, it is not possible to make contact with every segment of the perimeter of the canal and some portions may receive too much contact.
In any event, if the files are rotated passively in a laminar canal or a canal which has a laminar-type anatomy for most of its upper portion, the result is a circular opening whose diameter corresponds to that of the file that was used. The file typically stays in the center of the canal during rotation, such that the tip of each file acts like a fulcrum and xe2x80x9cideallyxe2x80x9d stays in the same position as a rotation point. Since each successive file can move less laterally, each file simply makes a bigger borehole than the preceding file. Accordingly, the files cannot clean a root canal without significantly altering the original anatomy by leaving a footprint or borehole corresponding to the configuration of the instruments used. More specifically, the result is a footprint or borehole with a perimeter that corresponds to the perimeter of the biggest file that extends well beyond the original anatomy of the root canal and yet in most instances does not adequately clean significant portions of the root canal.
Although, the crown-down technique typically enables a practitioner to more efficiently clean a root canal than the step-back technique, they both require the practitioner to utilize many different instruments. The need to frequently change the cleaning instrument results in significant time requirements for cleaning a root canal. However, careful instrumentation in accordance with either tedious time consuming method does not avoid the problems set forth above in relation to apical perforation, wall perforation, overthinning or failure to clean all of the wall surfaces.
Based on the foregoing observations, methods and systems are needed in the endodontic arts which enable a dental practitioner to remove and clean essentially all pulp material in a root canal requiring root canal therapy.
It would also be an advancement in the endodontic arts to provide methods and systems that are based on the three-dimensional reality of teeth and do not relate solely to buccolingual x-ray views, thereby enabling a practitioner to remove and clean pulp material in a root canal without compromising the strength of the walls and the apical anatomy.
It would also be a beneficial development in the endodontic arts to provide methods and systems which encourage perimetrical contact of the instruments with the canal walls.
Additionally, it would be an advancement in the endodontic arts to provide methods and systems that enable a practitioner to remove and clean pulp material in a root canal in a manner that is less likely to result in failure due to bacterial contamination, overly thinning the root canal, perforations or due to infected material being pushed beyond the root from the coronal aspects of canals.
Finally, it would also constitute progress in the endodontic arts to provide methods and systems which yield a predictable success rate, minimal risk of breaking an instrument, lower costs, and an abbreviated operating time or an operating time that is at least as efficient as conventional techniques.
An object of the present invention is to provide, methods and systems which enable a dental practitioner to remove and clean essentially all pulp material in a root canal requiring root canal therapy by progressively cleaning sections of the root canal from the crown to the apex.
Another object of the present invention is to provide methods and systems developed based on the three-dimensional reality of teeth and not just buccolingual x-ray views, thereby enabling a practitioner to remove and clean pulp material in a root canal without compromising the strength of the walls and the apical anatomy.
An additional object of the present invention is to provide methods and systems which encourage perimetrical contact of the instruments with the canal walls.
Additionally, another object of the present invention is to provide methods and systems that enable a practitioner to remove and clean pulp material in a root canal in a manner that is less likely to result in failure due to bacterial contamination, overly thinning the root canal, perforations or due to infected material being pushed beyond the root from the coronal aspects of canals.
Finally, it is an object of the present invention to provide methods and systems which yield a predictable success rate, minimal risk of breaking an instrument, lower costs, and an abbreviated operating time or an operating time that is at least as efficient as conventional techniques.
Some of the features of the invention which enable these objects to be achieved are as summarized hereinbelow after explaining some unique terminology used in the application. Applicant utilizes a terminology based on the methodology disclosed herein. The term xe2x80x9coperative root canalxe2x80x9d refers to the pathway which starts at the occlusal surface of the tooth, continues with the cameral wall segment and the anatomical canal per se, and finally reaches the foramen. Of course, the anatomical root canal extends from the pulp chamber or the floor of the pulp chamber to the apex. The operative root canal is divided into three sections or portions which are referred to herein as xe2x80x9cthe operative coronal portionxe2x80x9d, xe2x80x9cthe operative middle portionxe2x80x9d and xe2x80x9cthe apical portionxe2x80x9d. The operative coronal portion essentially includes the access cavity walls. The operative middle portion is the upper portion of the anatomical root canal while the apical portion is the lower portion of the anatomical root canal. A typical apical portion is the last or bottom 3 mm of the anatomical root canal.
The terms xe2x80x9coperative coronal portionxe2x80x9d, xe2x80x9coperative middle portionxe2x80x9d and xe2x80x9capical portionxe2x80x9d are unique terms that are distinct from the terminology conventionally utilized to refer to segments of a root canal. In the conventional crown-down method, the canal is customarily divided into the so-called xe2x80x9cthree thirdsxe2x80x9d, including: the crown, the middle third, and the apical third. In reference to the conventional crown-down method, it is common to use the term xe2x80x9ccoronal thirdxe2x80x9d to refer to the first part of the xe2x80x9canatomicalxe2x80x9d canal, originating at the floor of the pulp chamber or the upper limit of the middle third into which a tooth is customarily divided, with a theoretical line at the height of the neck.
During the root canal therapy, the pulp chamber can be opened to expose the anatomical root canal by any conventional method or instrument. Additionally, conventional methods and instruments can be used to prepare the operative coronal portion. However, unique methods and instruments are used in the operative middle portion while preferably simultaneously abrading the operative coronal portion. Additionally, after the operative middle portion has been cleaned, unique methods and instruments are used to improve access into the apical portion and to then clean the apical portion.
By envisioning the root canal as starting at the occlusal surface, practitioners can immediately identify any xe2x80x9cinterferencesxe2x80x9d or obstructions, as well as any protrusions of enamel, which may be disregarded. As a result, the instruments disclosed herein come into contact with every segment of the canal walls, including the obstructions, in order to achieve anatomical widening and also the rectification or straightening of the first two portions of the canal which include the operative coronal portion and the operative middle portion. This procedure opens the pathway for the preparation of the apical portion of the canal. The term xe2x80x9cinterferencexe2x80x9d refers to everything in the operative canal that hinders the rectilinear insertion of the instruments used, during the final cleaning phase of the procedure, preparation of the apical portion. The term xe2x80x9crectificationxe2x80x9d refers to the placement of the operative coronal portion or access cavity on the same axis as the operative middle portion. Rectification is achieved through the removal of interferences from the operative coronal portion and preferably from the operative middle portion of the operative canal as well.
The methodology disclosed herein involves the use of distinct instruments in the three portions of the anatomical root canal in different phases such that the root canal is cleaned progressively and sectionally. The instrument(s) associated with each phase have been designed specifically for that particular phase and accordingly have unique customized characteristics and features.
By cleaning the root canal in sections, the instruments can be adapted to the perimetrical or perimetral anatomy of the root canal. As a result, the entire perimeter or substantially all of the perimeter is contacted and cleaned along the length of the perimeter without substantially altering the configuration of the perimetrical anatomy. For example, a perimetrical anatomy that was primarily tubular or laminar will be enlarged but will still be primarily tubular or laminar. There will not be a large round borehole in the canal superimposed on the original perimetrical anatomy which corresponds to the diameter of the file that is used; as is the case with the nickel/titanium files used in crown down procedures that stay in the center of the canal even when the canal is laminar.
Additionally, the invention also enables the practitioner to prepare root canals in accordance with the anatomy of the root canal, even though the practitioner may not have been able to adequately identify the overall anatomy due to the inability to see the root canal as is the case from the mesial-distal view using standard radiography. Further, the invention also enables the practitioner to adapt to the contours of the root canal of all different types of teeth, by guiding instruments that have been designed to come into contact with every perimetrical segment of the walls.
Once the pulp chamber has been opened to expose the anatomical root canal, then the operative middle portion can be accessed. Before accessing the operative middle portion, however, it is necessary to determine the so-called xe2x80x9cworking lengthxe2x80x9d of the first two portions of the operative root canal including the operative middle portion and the operative coronal portion. The methods for identifying the working length involve the use of x-rays or videography, performed with the aid of a centering device and through use of the long-cone method After the working length has been determined, then the proper instruments can be selected for use in the preparation of the operative middle portion.
The working length is determined by measuring the canal axis from the occlusal plane, in order to arrive at the apical limit of the root as indicated on the x-ray. A distance of 3 mm is deducted from the measured length. The result is the maximum working depth that the operative middle portion instrument(s) should reach. The foregoing calculations also figure in the predetermination of the working lengths for all other instruments utilized in the procedure. The instruments preferably are selected to have files with lengths that are equal to the working length; however, stops may also be used to ensure that the files have the desired working length.
In addition to the anatomical widening of the perimeter of the operative middle portion, the preparation of the first two portions also involves the removal of the interferences from the operative coronal portion and the operative middle portions, thereby allowing the rectification of the first two portions of the operative root canal. Please note that during preparation of the operative middle portion and rectification of the first two portions, any and all intrusion of the instrument(s) into the apical portion is avoided. The boundary between the operative middle portion and the apical portion has been estimated to be located between 3 mm and 5 mm from the end of the root canal, as shown on the x-ray. After preparation of the operative middle portion and rectification of the first two portions have been completed, the procedure moves to the third stage, in which the apical portion is prepared.
After the working length has been determined for the first two portions including the operative coronal portion and the operative middle portion, the operator selects an instrument from a set of instruments designed for use in the operative middle portion. Each instrument in the set of instruments comprises a handle connected to a file with an abrasive surface or in other words a shaft with tines or an abrading portion. Each file in the set has the same length which is selected such that the operative middle portion of the operative root canal is cleaned without significantly removing pulp material from the apical root portion. Additionally, each file is designed to have a taper that is larger than the taper of each preceding file. Each file or shaft has an abrading portion for abrading the surfaces or walls of the root canal. In contrast to conventional files, as set forth in greater detail hereinbelow, the abrading portion may extend along the entire length of the file to enable the instrument to be used to clean the operative middle portion while also abrading the operative coronal portion.
The files of the instruments in the first set are preferably formed from stainless steel to enable the file to be moved in the desired manner. The files of the instruments in the first set are designed such that each file has sufficient flexibility to be flexed or curved to urge the abrading portion against the surfaces of the root canal and sufficient rigidity to apply pressure against the surfaces of the root canal as the abrading portion of the file is urged against the surfaces of the root canal and simultaneously moved in a cleaning motion. Additionally, the files have adequate resilience to avoid being substantially deformed as the file is flexed or curved to urge the file, particularly the abrading portion, against the surfaces of the root canal.
The contours of the perimeter of the root canal in the operative middle portion are followed as the file of the instrument(s) is flexed or curved against the surfaces of the root canal and simultaneously moved in a cleaning motion. Since the contours are followed, the perimeter is widened and smoothed but the original shape is not substantially altered.
After the operative middle portion has been cleaned, the apical portion may be cleaned by several different techniques or combinations thereof. One method involves no abrasive instrumentation within the apical portion just insertion of appropriate irrigation instruments. Since removal of the pulp material from the operative middle portion removes the majority of bacteria in the pulp canal, it has been found that it may not be necessary to abrade the apical portion.
Irrigants are delivered into the apical portion to maintain the debris derived from cleaning the root canal in suspension. The debris is then removed as the particles of the smear layer yielded from the action of the files used to prepare the canal may result in clogging the apical portion of the root canal with a plug. After the debris has been removed, the proper preparation and filling of the apical portion of the root canal can be achieved.
By eliminating or minimizing abrasive instrumentation within the apical portion, the potential for complications is diminished. As discussed above in the Background, most errors in performing root canals occur during instrumentation of the apical portion of the root canal. The apical portion is the most delicate part of the root canal and it is the most distally located Accordingly, it is highly advantageous to just irrigate and then remove the irrigant and debris, since many complications occur during abrasive instrumentation.
However, in some instances, it may be necessary to improve access into the apical portion such that an irrigation needle can be deployed to deliver irrigants to the apical portion. Access into the apical portion is improved by widening, for example, at least the entrance of the apical portion or the entire apical portion.
Alternatively, another method involves the use of a set of instruments designed for cleaning the apical portion in an abrasive manner. Such a method may be initiated directly after the operative middle portion of the operative root canal has been cleaned. However, it may be necessary to have two phases of instrumentation within the apical portion of the operative root canal including widening and abrasive cleaning of the apical portion. More particularly, it may be necessary to improve the access into the apical portion before performing the abrasive instrumentation by widening the transition between the operative middle portion and the apical portion to enable irrigants to be delivered into the apical portion.
These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.